While problems in global environment and energy are becoming serious, a solar battery has attracted attention as an energy source of clean and causing no depletion. When using the solar battery outside such as on the part of a building roof, it is general to be used in the form of a solar battery module.
In general, the solar battery module has a constitution in which a solar battery cell formed from multicrystalline silicon or the like is superposed and laminated between solar battery sealing materials formed from a soft and transparent resin, and both the front-back surfaces of the laminate is covered with a protective sheet for a solar battery module. That is, a typical solar battery module has a lamination configuration of a protective sheet for solar battery module (front surface protecting sheet)/a sheet for sealing a solar battery/a solar battery cell/a sheet for sealing a solar battery/a protective sheet for solar battery module (back surface protecting sheet). As a result, the solar battery module has a weather resistant property, and is suitable for the outside use such as the use at the roof of a building and the like.
In the past, an ethylene.vinyl acetate copolymer (EVA) has been widely used as a material forming the sheet for sealing a solar battery (sealing material for solar battery) because of its transparency, flexibility, and the like (for example, see Patent Document 1). When the ethylene.vinyl acetate copolymer is used as a solar battery sealing material, it is general to perform a cross-linking treatment to give sufficient heat resistance. However, the cross-linking treatment requires a comparatively long period of time of about 1 to 2 hours, which thus has become the cause of lowering a production rate and production efficiency of a solar battery module. In addition, it has been concerned that a component of acetic acid gas or the like, which is generated when EVA is decomposed, may possibly have an impact on a solar battery element.
As one of the means for solving aforementioned technical problems, there can be mentioned a use of an olefin-based (co)polymer as at least one part of a solar battery sealing material, and also there is a proposal about a solar battery sealing material having an olefin-based (co)polymer (see Patent Document 2). However, the Patent Document 2 is not disclosing any specific guidelines for kinds of the olefin-based (co)polymer and embodiment of usage, for obtaining desired properties (flexibility, stress absorbing property, transparency, impact resistant strength at low temperature, etc.) as a sealing material. It can be thought that the technology disclosed in the Patent Document 2 is based on an assumption that there is a cross-linking treatment, and is to achieve the desired properties in conjunction with the cross-linking treatment.
Patent Document 1: Japanese Patent Unexamined Publication No. H8-283696
Patent Document 2: Japanese Patent Unexamined Publication No. 2000-091611